Flip a Coin

How to use the coin flipper

Choose how many coins to toss (1 to 10) and press Flip, tap a coin, or press the space bar. Gold is heads and silver is tails, and the result is also written out in words and read aloud by screen readers. The tally counts every coin you toss, tracks your current and longest streak, and shows the last 60 results in order. Reset tally starts again. The page address keeps your last flip and your best streak, so Share this result sends a friend a link that shows your flip and challenges them to beat your streak. If your device is set to reduce motion, the coins change without spinning.

How the flip is decided

For each coin the page asks crypto.getRandomValues — the cryptographically secure random generator built into your browser — for a whole number from 0 to 4,294,967,295. Even numbers mean heads, odd numbers mean tails. Because exactly half of the 4,294,967,296 possible values are even, the chance of heads is exactly one half, with no rounding and no bias, and each coin is independent of every other coin and every earlier flip. With several coins, the number of heads follows the binomial distribution:

P(heads) = 2,147,483,648 ÷ 4,294,967,296 = 1/2 P(exactly k heads with n coins) = C(n, k) ÷ 2ⁿ C(n, k) = n! ÷ (k! × (n − k)!)

Worked example: three coins

Three coins can land in 2 × 2 × 2 = 8 equally likely orders: HHH, HHT, HTH, THH, HTT, THT, TTH and TTT. Exactly two heads appears in three of them (HHT, HTH, THH), so C(3, 2) = 3 and the chance is 3 ÷ 8 = 37.5% — the same number the working shows when you flip 3 coins and get 2 heads. All heads or all tails is 1 ÷ 8 = 12.5% each. With 10 coins, exactly 5 heads — the “expected” result — happens only 252 ÷ 1,024 = 24.61% of the time: most flips of ten coins are not an even split, and the odds table under the tally shows every possibility.

Streaks are normal

Runs of the same side feel suspicious, but they are exactly what randomness looks like. The tally shows the chance of a streak at least as long as your best one in the number of tosses you have made, computed exactly with a recursion of the kind described by Mark Schilling in The Longest Run of Heads (1990). Counting streaks of either side:

Each doubling of the number of tosses adds about one to the typical longest streak. A streak does not change what happens next: after any run, the next toss is still 50/50.

Are real coin tosses fair?

Almost, but not quite. In 2007 the mathematicians Persi Diaconis, Susan Holmes and Richard Montgomery analyzed the physics of a hand-caught toss and predicted that a coin lands on the same side it started about 51% of the time, because a flipped coin wobbles as it spins. A team led by František Bartoš tested this with 350,757 flips by 48 people, published in the Journal of the American Statistical Association in 2025. Coins landed on their starting side 50.8% of the time (95% credible interval 50.6% to 50.9%), while heads overall came up 50.0% — so heads and tails were balanced, but the starting side had a small edge that varied between flippers. A virtual flip has no starting side and no wobble, so it is exactly 50/50. For another quick random decision, try the dice roller.